Description: NMEA messages consist of various fields. The fields are:
• Header
• Special format fields
• Numeric value fields
• Information fields
• Null fields
Certain symbols are used as identifier for the field types. These symbols are described in this section.
Header 
Special format fields
Numeric value fields
Information fields
Null fields
☞ Fields are always separated by a comma. Before the Checksum field there is never a comma.
☞ When information for a field is not available, the position in the data string is empty.